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.TH SEM_INIT 3C "Jul 9, 2009"
.SH NAME
sem_init \- initialize an unnamed semaphore
.SH SYNOPSIS
.LP
.nf
#include <semaphore.h>

\fBint\fR \fBsem_init\fR(\fBsem_t *\fR\fIsem\fR, \fBint\fR \fIpshared\fR, \fBunsigned int\fR \fIvalue\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBsem_init()\fR function is used to initialize the unnamed semaphore
referred to by \fIsem\fR. The value of the initialized semaphore is
\fIvalue\fR. Following a successful call to \fBsem_init()\fR, the semaphore may
be used in subsequent calls to \fBsem_wait\fR(3C), \fBsem_trywait\fR(3C),
\fBsem_post\fR(3C), and \fBsem_destroy\fR(3C). This semaphore remains usable
until the semaphore is destroyed.
.sp
.LP
If the \fIpshared\fR argument has a non-zero value, then the semaphore is
shared between processes; in this case, any process that can access the
semaphore \fIsem\fR can use \fIsem\fR for performing \fBsem_wait\fR(3C),
\fBsem_trywait\fR(3C), \fBsem_post\fR(3C), and \fBsem_destroy\fR(3C)
operations.
.sp
.LP
Only \fIsem\fR itself may be used for performing synchronization. The result of
referring to copies of \fIsem\fR in calls to \fBsem_wait\fR(3C),
\fBsem_trywait\fR(3C), \fBsem_post\fR(3C), and \fBsem_destroy\fR(3C), is
undefined.
.sp
.LP
If the \fIpshared\fR argument is zero, then the semaphore is shared between
threads of the process; any thread in this process can use \fIsem\fR for
performing \fBsem_wait\fR(3C), \fBsem_trywait\fR(3C), \fBsem_post\fR(3C), and
\fBsem_destroy\fR(3C) operations. The use of the semaphore by threads other
than those created in the same process is undefined.
.sp
.LP
Attempting to initialize an already initialized semaphore results in undefined
behavior.
.sp
.LP
The \fBsem_open\fR(3C) function is used with named semaphores.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, the function initializes the semaphore in
\fIsem\fR. Otherwise, it returns \fB\(mi1\fR and sets \fBerrno\fR to indicate
the error.
.SH ERRORS
.sp
.LP
The \fBsem_init()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 11n
The \fIvalue\fR argument exceeds  \fBSEM_VALUE_MAX\fR.
.RE

.sp
.ne 2
.na
\fB\fBENOSPC\fR \fR
.ad
.RS 11n
A resource required to initialize the semaphore has been exhausted, or the
resources have reached the limit on semaphores (\fBSEM_NSEMS_MAX\fR).
.RE

.sp
.ne 2
.na
\fB\fBENOSYS\fR \fR
.ad
.RS 11n
The \fBsem_init()\fR function is not supported by the system.
.RE

.sp
.ne 2
.na
\fB\fBEPERM\fR \fR
.ad
.RS 11n
The process lacks the appropriate privileges to initialize the semaphore.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
_
Standard	See \fBstandards\fR(7).
.TE

.SH SEE ALSO
.sp
.LP
.BR sem_destroy (3C),
.BR sem_open (3C),
.BR sem_post (3C),
.BR sem_wait (3C),
.BR attributes (7),
.BR standards (7)
